Switching via a bus datagram from input port memory to output port memory via a shared bus 巴日 bus contention:switching 日日日目 speed limited by bus bandwidth bus 32 Gbps bus,Cisco 5600: sufficient speed for access and enterprise routers Network Layer 4-26
Network Layer 4-26 Switching via a bus datagram from input port memory to output port memory via a shared bus bus contention: switching speed limited by bus bandwidth 32 Gbps bus, Cisco 5600: sufficient speed for access and enterprise routers bus
Switching via interconnection network overcome bus bandwidth limitations banyan networks,crossbar,other interconnection nets initially 巨日 developed to connect processors 巨日B in multiprocessor 巨日日 advanced design:fragmenting crossbar datagram into fixed length cells, switch cells through the fabric. Cisco 12000:switches 60 Gbps through the interconnection network Network Layer 4-27
Network Layer 4-27 Switching via interconnection network overcome bus bandwidth limitations banyan networks, crossbar, other interconnection nets initially developed to connect processors in multiprocessor advanced design: fragmenting datagram into fixed length cells, switch cells through the fabric. Cisco 12000: switches 60 Gbps through the interconnection network crossbar
Output ports This slide in HUGELY important! datagram switch buffer link fabric layer line protocol termination queueing (send) buffering require Datagram (packets)can be lost arrive from fabri due to congestion,lack of buffers transmission rate schedulin Priority scheduling -who gets best queued d performance,network neutrality Network Layer 4-28
Network Layer 4-28 Output ports buffering required when datagrams arrive from fabric faster than the transmission rate scheduling discipline chooses among queued datagrams for transmission line termination link layer protocol (send) switch fabric datagram buffer queueing This slide in HUGELY important! Datagram (packets) can be lost due to congestion, lack of buffers Priority scheduling – who gets best performance, network neutrality
Output port queueing fabric/ at t,packets more one packet time later from input to output buffering when arrival rate via switch exceeds output line speed *queueing(delay)and loss due to output port buffer overflow! Network Layer 4-29
Network Layer 4-29 Output port queueing buffering when arrival rate via switch exceeds output line speed queueing (delay) and loss due to output port buffer overflow! at t, packets more from input to output one packet time later switch fabric switch fabric
How much buffering? RFC 3439 rule of thumb:average buffering equal to "typical"RTT (say 250 msec)times link capacity C e.g.,C=10 Gpbs link:2.5 Gbit buffer recent recommendation:with N flows, buffering equal to RTT.C N Network Layer 4-30
Network Layer 4-30 How much buffering? RFC 3439 rule of thumb: average buffering equal to “typical” RTT (say 250 msec) times link capacity C e.g., C = 10 Gpbs link: 2.5 Gbit buffer recent recommendation: with N flows, buffering equal to RTT C. N