1、项目编号 ITTEL_R other devices may be passive such as a CSU/DSU. Regardless of constituent components, the system is treated as a singular entity to which stimulus is offered and response measured. Measurement units: n/a Issues: See Also: device under test (DUT) (3.1.1) 3.2 Traffic orientation This grou
2、p of definitions applies to the traffic presented to the interfaces of a DUT/SUT and indicates whether the interfaces are receiving only, transmitting only, or both receiving and transmitting. 3.2.1 Unidirectional traffic Definition: When all frames presented to the input interfaces of a DUT/SUT are
3、 addressed to output interfaces which do not themselves receive any frames. 北京国信网安信息系统测评技术试验室 Beijing GuoXinWangAn Information Technology Testing&Evaluation Laboratory Benchmarking Terminology for LAN Switching Devices 第 4 页 共 20 页 Discussion: This definition conforms to the discussion in section 16
4、 of RFC 1944 which describes how unidirectional traffic can be offered to a DUT/SUT to measure throughput. Unidirectional traffic is also appropriate for: -the measurement of the minimum inter-frame gap -the creation of many-to-one or one-to-many interface overload -the detection of head of line blo
5、cking -the measurement of forwarding rates and throughput when congestion control mechanisms are active. When a tester offers unidirectional traffic to a DUT/SUT reception and transmission are handled by different interfaces or sets of interfaces of the DUT/SUT. All frames received from the tester b
6、y the DUT/SUT are transmitted back to the tester from interfaces which do not themselves receive any frames. It is useful to distinguish traffic orientation and traffic distribution when considering traffic patterns used in device testing. Unidirectional traffic, for example, is traffic orientated i
7、n a single direction between mutually exclusive sets of source and destination interfaces of a DUT/SUT. Such traffic, however, can be distributed between interfaces in different ways. When traffic is sent to two or more interfaces from an external source and then forwarded by the DUT/SUT to a single
8、 output interface the traffic orientation is unidirectional and the traffic distribution between interfaces is many-to-one. Traffic can also be sent to a single input interface and forwarded by the DUT/SUT to two or more output interfaces to achieve a one-to-many distribution of traffic. Such traffi
9、c distributions can also be combined to test for head of line blocking or to measure forwarding rates and throughput when congestion control mechanisms are active. When a DUT/SUT is equipped with interfaces running at different media rates the number of input interfaces required to load or overload
10、an output interface or interfaces will vary. It should be noted that measurement of the minimum inter-frame gap serves to detect violations of the IEEE 802.3 standard. Issues: half duplex / full duplex Measurement units: n/a See Also: bidirectional traffic (3.2.2) non-meshed traffic (3.3.1) partiall
11、y meshed traffic (3.3.2) fully meshed traffic (3.3.3) congestion control (3.7) 北京国信网安信息系统测评技术试验室 Beijing GuoXinWangAn Information Technology Testing&Evaluation Laboratory Benchmarking Terminology for LAN Switching Devices 第 5 页 共 20 页 head of line blocking (3.7.3) 3.2.2 Bidirectional traffic Definit
12、ion: Frames presented to a DUT/SUT such that every receiving interface also transmits. Discussion: This definition conforms to the discussion in section 14 of RFC 1944. When a tester offers bidirectional traffic to a DUT/SUT all the interfaces which receive frames from the tester also transmit frame
13、s back to the tester. Bidirectional traffic MUST be offered when measuring the throughput or forwarding rate of full duplex interfaces of a switching device. Issues: truncated binary exponential back-off algorithm Measurement units: n/a See Also: unidirectional traffic (3.2.1) non-meshed traffic (3.
14、3.1) partially meshed traffic (3.3.2) fully meshed traffic (3.3.3) 3.3 Traffic distribution This group of definitions applies to the distribution of frames forwarded by a DUT/SUT. 3.3.1 Non-meshed traffic Definition: Frames offered to a single input interface and addressed to a single output interfa
15、ce of a DUT/SUT where input and output interfaces are grouped in mutually exclusive pairs. Discussion: In the simplest instance of non-meshed traffic all frames are offered to a single input interface and addressed to a single output interface. The one-to-one mapping of input to output interfaces re
16、quired by non-meshed traffic can be extended to multiple mutually exclusive pairs of input and output interfaces. Measurement units: n/a Issues: half duplex / full duplex 北京国信网安信息系统测评技术试验室 Beijing GuoXinWangAn Information Technology Testing&Evaluation Laboratory Benchmarking Terminology for LAN Swit
17、ching Devices 第 6 页 共 20 页 See Also: unidirectional traffic (3.2.1) bidirectional traffic (3.2.2) partially meshed traffic (3.3.2.) fully meshed traffic (3.3.3) burst (3.4.1) 3.3.2 Partially meshed traffic Definition: Frames offered to one or more input interfaces of a DUT/SUT and addressed to one o
18、r more output interfaces where input and output interfaces are mutually exclusive and mapped one-to-many, many- to-one or many-to-many. Discussion: This definition follows from the discussion in section 16 of RFC 1944 on multi-port testing. Partially meshed traffic allows for one-to-many, many-to-on
19、e or many-to-many mappings of input to output interfaces and readily extends to configurations with multiple switching devices linked together over backbone connections. It should be noted that partially meshed traffic can load backbone connections linking together two switching devices or systems m
20、ore than fully meshed traffic. When offered partially meshed traffic devices or systems can be set up to forward all of the frames they receive to the opposite side of the backbone connection whereas fully meshed traffic requires at least some of the offered frames to be forwarded locally, that is t
21、o the interfaces of the DUT/SUT receiving them. Such frames will not traverse the backbone connection. Measurement units: n/a Issues: half duplex / full duplex See Also: unidirectional traffic (3.2.1) bidirectional traffic (3.2.2) non-meshed traffic (3.3.1) fully meshed traffic (3.3.3) burst (3.4.1)
22、 3.3.3 Fully meshed traffic Definition: Frames offered to a designated number of interfaces of a DUT/SUT such that each one 北京国信网安信息系统测评技术试验室 Beijing GuoXinWangAn Information Technology Testing&Evaluation Laboratory Benchmarking Terminology for LAN Switching Devices 第 7 页 共 20 页 of the interfaces un
23、der test receives frames addressed to all of the other interfaces under test. Discussion: As with bidirectional partially meshed traffic, fully meshed traffic requires each one the interfaces of a DUT/SUT to both receive and transmit frames. But since the interfaces are not divided into groups as wi
24、th partially meshed traffic every interface forwards frames to and receives frames from every other nterface. The total number of individual input/output interface pairs when traffic is fully meshed over n switched interfaces equals n x (n - 1). This compares with n x (n / 2) such interface pairs wh
25、en traffic is partially meshed. Fully meshed traffic on half duplex interfaces is inherently bursty since interfaces must interrupt transmission whenever they receive frames. This kind of bursty meshed traffic is characteristic of real network traffic and can be advantageously used to diagnose a DUT
26、/SUT by exercising many of its component arts simultaneously. Additional inspection may be warranted to correlate the frame forwarding capacity of a DUT/SUT when offered meshed traffic and the behavior of individual elements such as input or output buffers, buffer allocation mechanisms, aggregate sw
27、itching capacity, processing speed or medium access control. The analysis of forwarding rate measurements presents a challenge when offering bidirectional or fully meshed traffic since the rate at which the tester can be observed to transmit frames to the DUT/SUT may be smaller than the rate at whic
28、h it intends to transmit due to collisions on half duplex media or the action of congestion control mechanisms. This makes it important to take account of both the intended and offered loads defined in sections 3.5.1.and 3.5.2 below when reporting the results of such forwarding rate measurements. Wh
29、en offering bursty meshed traffic to a DUT/SUT a number of variables have to be considered. These include frame size, the number of frames within bursts, the interval between bursts as well as the distribution of load between incoming and outgoing traffic. Terms related to bursts are defined in sect
30、ion 3.4 below. Measurement units: n/a Issues: half duplex / full duplex See Also: unidirectional traffic (3.2.1) bidirectional traffic (3.2.2) non-meshed traffic (3.3.1) partially meshed traffic (3.3.2) burst (3.4.1) 北京国信网安信息系统测评技术试验室 Beijing GuoXinWangAn Information Technology Testing&Evaluation La
31、boratory Benchmarking Terminology for LAN Switching Devices 第 8 页 共 20 页 intended load (3.5.1) offered load (3.5.2) 3.4 Bursts This group of definitions applies to the intervals between frames or groups of frames offered to the DUT/SUT. 3.4.1 Burst Definition: A sequence of frames transmitted with t
32、he minimum legal inter-frame gap. Discussion: This definition follows from discussions in section 3.16 of RFC1242 and section 21 of RFC 1944 which describes cases where it is useful to consider isolated frames as single frame bursts. Measurement units: n/a Issues: See Also: burst size (3.4.2) inter-
33、burst gap (IBG) (3.4.3) 3.4.2 Burst size Definition: The number of frames in a burst. Discussion: Burst size can range from one to infinity. In unidirectional traffic as well as in bidirectional or meshed traffic on full duplex interfaces there is no theoretical limit to burst length. When traffic i
34、s bidirectional or meshed bursts on half duplex media are finite since interfaces interrupt transmission intermittently to receive frames. On real networks burst size will normally increase with window size.his makes it desirable to test devices with small as well as large burst sizes. Measurement u
35、nits: number of N-octet frames Issues: See Also: burst (3.4.1) inter-burst gap (IBG) (3.4.3) 北京国信网安信息系统测评技术试验室 Beijing GuoXinWangAn Information Technology Testing&Evaluation Laboratory Benchmarking Terminology for LAN Switching Devices 第 9 页 共 20 页 3.4.3 Inter-burst gap (IBG) Definition: The interva
36、l between two bursts. Discussion: This definition conforms to the discussion in section 20 of RFC1944 on bursty traffic. Bidirectional and meshed traffic are inherently bursty since interfaces share their time between receiving and transmitting frames. External sources offering bursty traffic for a
37、given frame size and burst size must adjust the inter-burst gap to achieve a specified average rate of frame transmission. Measurement units: nanoseconds microseconds milliseconds seconds Issues: See Also: burst (3.4.1) burst size (3.4.2) 3.5 Loads This group of definitions applies to the rates at w
38、hich traffic is offered to any DUT/SUT. 3.5.1 Intended load (Iload) Definition: The number of frames per second that an external source attempts to transmit to a DUT/SUT for forwarding to a specified output interface or interfaces. Discussion: Collisions on CSMA/CD links or the action of congestion
39、control mechanisms can effect the rate at which an external source of traffic transmits frames to a DUT/SUT. This makes it useful to distinguish the load that an external source attempts to apply toa DUT/SUT and the load it is observed or measured to apply. In the case of Ethernet an external source
40、 of traffic MUST implement the truncated binary exponential back-off algorithm to ensure that it is accessing the medium legally. Measurement units: bits per second N-octets per second (N-octets per second / media_maximum-octets per second) x 100 北京国信网安信息系统测评技术试验室 Beijing GuoXinWangAn Information Te
41、chnology Testing&Evaluation Laboratory Benchmarking Terminology for LAN Switching Devices 第 10 页 共 20 页 Issues: See Also: burst (3.4.1) inter-burst gap (3.4.3) offered load (3.5.2) 3.5.2 Offered load (Oload) Definition: The number of frames per second that an external source can be observed or measu
42、red to transmit to a DUT/SUT for forwarding to a specified output interface or interfaces. Discussion: The load which an external device can be observed to apply to a DUT/SUT may be less than the intended load due to collisions on half duplex media or the action of congestion control mechanisms.This
43、 makes it important to distinguish intended and offered load when analyzing the results of forwarding rate measurements using bidirectional or fully meshed traffic. Frames which are not successfully transmitted by an external source of traffic to a DUT/SUT MUST NOT be counted as transmitted frames w
44、hen measuring forwarding rates. The frame count on an interface of a DUT/SUT may exceed the rate at which an external device offers frames due to the presence of spanning tree BPDUs (Bridge Protocol Data Units) on 802.1D-compliant switches or SNMP frames. Such frames should be treated as modifiers a
45、s described in section 11 of RFC 1944. Offered load MUST be indicated when reporting the results of forwarding rate measurements. Measurement units: bits per second N-octets per second (N-octets per second / media_maximum-octets per second) x 100 Issues: token ring See Also: bidirectional traffic (3.2.2) fully meshed traffic (3.3.3) intended load (3.5.1) forwarding rate (3.6.1)
