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2 Problem: Multi-hop communication parallelism via packet-switching Consider a multi-hop network path between a sending station X to a receiving station Y. Given an application- data (ADU) of length I bits that needs to be sent/received, the packetization layer in X segments the I-bit ADU into smaller packets of length R bits each to attain higher efficiency of data transfer to Y over the multiple hops (where R I). The number of packets transferred is: [1. Efficiency improvement arises due to the parallelism in packet transfers by the store-and-forward packet-switches in different hops of the path. The store-and-forward function (which typically resides in a network-layer router) receives a packet on the incoming link, stores the packet in a memory buffer, and then forwards this packet on the outgoing link (when/if the link is idle). Given a logical data-path connecting X to Y through a series of routers, the store-and-forward function of a router r meets two inter-woven goals when connecting its incoming and outgoing links in the patha: (i): Harmonizes any difference in the transfer speeds of incoming and outgoing links of r with a packet- buffering capability; (ii): Parallelizes the transmission of a packet on the outgoing link of r (towards Y) with the arrival of a next packet q (from X) on the incoming link of r. Besides communication parallelism, the packetization of application data units (ADU) enables parallelism even between the end-user data generation/consumption and the network data transport activities. For e.g., a 50-page New York Times newspaper is treated as a single ADU, with each of the NYT pages as a distinct packet. When the user reads page #1, the system transports pages #2, #3, etc (via a delivery truck or web download); likewise, when page #25 is being read (say), the remaining pages #26, #27, etc are in transit. This parallelism achieves more time-efficiency when compared to a case where the end-user waits until the 50-page NYT is made available in entirety before even starting the read of NYT (from page #1). 2The terms "incoming" and "outgoing" are w.r.t. to the direction of ADU flow. The logical-path is itself bidirectional i.e., packets can flow from X to Y or from Y to X. software routing layer at sender at sender routing layer at receiver software at receiver ADU I (7 bits long) intermediate packet router (store & forward) command to send(d) tx packet Computer: (at sender) (at receiver) App. App software software C: link capacity packet tx in bits/sec layer link router link layer hop R+h header of Size h bits Te = C enerate data-unit (ADU): video/audio-clip) 7+h Tox= c is different from TT.T. (note: T ADU transfer delay. in network (end-to-end): D Input arrivals and ano le spuis inding incoming packet is held in a butler liste being forwarded) kejap supremios time m . th Trx = 6 Anducerdend-to-end transfer delay D d3 ADU is sent as it is (ie, as a long packet) Tprop hop 2 reduction in data-transfer delay hop 1 (D-D) received computation to With communication parallelism hop 2 arising from packetization of ADU process ADU d Pat receiver device (i.e., breaking d into smaller packets of size" Reach that can be transmitted host computer (at receiver) R ADU transfer delay. in network (end-to-end): D Input arrivals and ano le spuis inding incoming packet is held in a butler liste being forwarded) kejap supremios time m . th Trx = 6 Anducerdend-to-end transfer delay D d3 ADU is sent as it is (ie, as a long packet) Tprop hop 2 reduction in data-transfer delay hop 1 (D-D) received computation to With communication parallelism hop 2 arising from packetization of ADU process ADU d Pat receiver device (i.e., breaking d into smaller packets of size" Reach that can be transmitted host computer (at receiver) R